• Title/Summary/Keyword: axial cracks

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J Estimations For Axial Surface Cracked Pipes Under Pressure (축방향 표면균열이 존재하고 내압을 받는 직관의 J 예측 방법)

  • Oh, Chang-Sik;Song, Tae-Kwang;Kim, Yun-Jae
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.1824-1829
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    • 2007
  • In the present paper, limit pressures for axial surface cracked pipe are proposed, and a reference stress based J estimation method is also provided based on the proposed limit pressure solutions. Employed cracks are assumed to be constant-depth, internal surface cracks, and wide ranges of variables are considered.

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The control method for axial cracks on NATM tunnel linings (NATM 터널라이닝 종방향 균열 제어공법)

  • Zheng, Xiu-Mei;Park, Inn-Joon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.11 no.4
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    • pp.437-447
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    • 2009
  • It is easily found by several references of NATM that the cracks on the lining concrete of NATM are more developed than those of the conventional tunnel methods. Based on the results of research, the new method is proposed to control and protect the axial cracks on the tunnel linings. Also, the efficiency of proposed method is evaluated using the Distinct Element Method.

Estimation of Axial Nail Force Considering Cracks and Creeps of Grout (그라우트의 균열 및 Creep 현상을 고려한 쏘일네일의 축인장력 산정)

  • 임유진;황상기
    • Proceedings of the Korean Geotechical Society Conference
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    • 2000.11a
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    • pp.159-166
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    • 2000
  • A new method of estimating axial nail force is proposed. An instrumented soil nail wall is selected to investigate the effectiveness of the new proposed method. The new method includes effect of creep and age of cement grout surrounding the steel bar, The new method also considers cracks in the grout generated during and after the end of the wall construction. It is found from this study that a reduced grout stiffness due to creep with age and crack of the grout must be considered for estimating correct axial nail forces. The reduced grout stiffness is considered also providing significant part of axial nail load compared to that of steel bar.

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Development of Optimum Global Failure Prediction Model for Steam Generator Tube with Two Parallel Cracks (평행한 두 개의 균열이 존재하는 증기발생기 세관의 최적 광범위파손 예측모델 개발)

  • Moon Seong ln;Chang Yoon Suk;Lee Jin Ho;Song Myung Ho;Choi Young Hwan;Kim Joung Soo;Kim Young Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.5 s.236
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    • pp.754-761
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    • 2005
  • The 40\% of wall thickness criterion which has been used as a plugging rule of steam generator tubes is applicable only to a single cracked tube. In the previous studies performed by authors, several global failure prediction models were introduced to estimate the failure loads of steam generator tubes containing two adjacent parallel axial through-wall cracks. These models were applied for thin plates with two parallel cracks and the COD base model was selected as the optimum one. The objective of this study is to verify the applicability of the proposed optimum global failure prediction model for real steam generator tubes with two parallel axial through-wall cracks. For the sake of this, a series of plastic collapse tests and finite element analyses have been carried out fur the steam generator tubes with two machined parallel axial through-wall cracks. Thereby, it was proven that the proposed optimum failure prediction model can be used as the best one to estimate the failure load quite well. Also, interaction effects between two adjacent cracks were assessed through additional finite element analyses to investigate the effect on the global failure behavior.

An experimental study on fracture coalescence characteristics of brittle sandstone specimens combined various flaws

  • Yang, Sheng-Qi
    • Geomechanics and Engineering
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    • v.8 no.4
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    • pp.541-557
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    • 2015
  • This research aims to analyze the fracture coalescence characteristics of brittle sandstone specimen ($80{\times}160{\times}30mm$ in size) containing various flaws (a single fissure, double squares and combined flaws). Using a rock mechanics servo-controlled testing system, the strength and deformation behaviours of sandstone specimen containing various flaws are experimentally investigated. The results show that the crack initiation stress, uniaxial compressive strength and peak axial strain of specimen containing a single fissure are all higher than those containing double squares, while which are higher than those containing combined flaws. For sandstone specimen containing combined flaws, the uniaxial compressive strength of sandstone increase as fissure angle (${\alpha}$) increases from $30^{\circ}$ to $90^{\circ}$, which indicates that the specimens with steeper fissure angles can support higher axial capacity for ${\alpha}$ greater than $30^{\circ}$. In the entire deformation process of flawed sandstone specimen, crack evolution process is discussed detailed using photographic monitoring technique. For the specimen containing a single fissure, tensile wing cracks are first initiated at the upper and under tips of fissure, and anti-tensile cracks and far-field cracks are also observed in the deformation process; moreover anti-tensile cracks usually accompanies with tensile wing cracks. For the specimen containing double squares, tensile cracks are usually initiated from the top and bottom edge of two squares along the direction of axial stress, and in the process of final unstable failure, more vertical splitting failures are observed in the ligament region. When a single fissure and double squares are formed together into combined flaws, the crack coalescence between the fissure tips and double squares plays a significant role for ultimate failure of the specimen containing combined flaws.

Evaluation of Eddy Current Signals from the Inner Wall Axial Cracks of Steam Generator Tubes (증기발생기 전열관의 내면 축방향 균열에 대한 ECT 특성 평가)

  • Choi, Myung-Sik;Hur, Do-Haeng;Lee, Doek-Hyun;Park, Jung-Am;Han, Jung-Ho
    • Journal of the Korean Society for Nondestructive Testing
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    • v.21 no.5
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    • pp.501-509
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    • 2001
  • For the enhancement of ECT reliability on the primary water stress corrosion cracks of nuclear steam generator tubes, of which the occurrence is on the increase, it is important to comprehend the signal characteristics on crack morphology and to select an appropriate probe type. In this paper, the sizing accuracy and the detectability for the inner wall axial cracks of tubes were quantitatively evaluated using the following specimens: the electric discharge machined notches and the corrosion cracks which were developed on the operating steam generator tubes. The difference of eddy current signal characteristics between pancake and axial coil were also Investigated. The results obtained from this study provide a useful information for more precise evaluation on the inner wall axial tracks oi stram generator tubes.

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Constraint-corrected fracture mechanics analysis of nozzle crotch corners in pressurized water reactors

  • Kim, Jong-Sung;Seo, Jun-Min;Kang, Ju-Yeon;Jang, Youn-Young;Lee, Yun-Joo;Kim, Kyu-Wan
    • Nuclear Engineering and Technology
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    • v.54 no.5
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    • pp.1726-1746
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    • 2022
  • This paper presents fracture mechanics analysis results for various cracks located at pressurized water reactor pressure vessel nozzle crotch corners taking into consideration constraint effect. Technical documents such as the ASME B&PV Code, Sec.XI were reviewed and then a fracture mechanics analysis procedure was proposed for structural integrity assessment of various nozzle crotch corner cracks under normal operation conditions considering the constraint effect. Linear elastic fracture mechanics analysis was performed by conducting finite element analysis with the proposed analysis procedure. Based on the evaluation results, elastic-plastic fracture mechanics analysis taking into account the constraint effect was performed only for the axial surface crack of the reactor pressure vessel outlet nozzle with cladding. The fracture mechanics analysis result shows that only the axial surface crack in the reactor pressure vessel outlet nozzle has the stress intensity factor exceeding the low bound of upper-shelf fracture toughness irrespectively of considering the constraint effect. It is confirmed that the J-integral for the axial crack of the outlet nozzle does not exceed the ductile crack initiation toughness. Hence, it can be ensured that the structural integrity of all the cracks is maintained during the normal operation.

A transfer matrix method for in-plane bending vibrations of tapered beams with axial force and multiple edge cracks

  • Lee, Jung Woo;Lee, Jung Youn
    • Structural Engineering and Mechanics
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    • v.66 no.1
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    • pp.125-138
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    • 2018
  • This paper proposes a transfer matrix method for the bending vibration of two types of tapered beams subjected to axial force, and it is applied to analyze tapered beams with an edge or multiple edge open cracks. One beam type is assumed to be reduced linearly in the cross-section height along the beam length. The other type is a tapered beam in which the cross-section height and width with the same taper ratio is linearly reduced simultaneously. Each crack is modeled as two sub-elements connected by a rotational spring, and the method can evaluate the effect of cracking on the desired number of eigenfrequencies using a minimum number of subdivisions. Among the power series available for the solutions, the roots of the differential equation are computed using the Frobenius method. The computed results confirm the accuracy of the method and are compared with previously reported results. The effectiveness of the proposed methods is demonstrated by examining specific examples, and the effects of cracking and axial loading are carefully examined by a comparison of the single and double tapered beam results.

Detectability and Sizing Ability of Rotating Pancake Coil Technique for Cracks in Steam Generator Tubes

  • Y. M. Cheong;K. W. Kang;Lee, Y. S.;T. E. Chung
    • Nuclear Engineering and Technology
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    • v.30 no.4
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    • pp.377-385
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    • 1998
  • Many nuclear power plants have experienced unscheduled shutdown due to the leakage of steam generator tubes. The leakages are normally due to the crack, possibly stress corrosion cracking (SCC) near the tube expansion at the top of tubesheet or at the tangential point of the row-1 U-bend region. The conventional eddy current technique, which makes use of a differential bobbin coil, has been found to be inadequate for the early detection of SCC. During the in-service inspection, therefore, it is a general practice that the rotating pancake coil (RPC) is used for detecting the cracks. Even in using RPC, however, it is difficult to determine the depth of the cracks quantitatively. This paper attempts to determine the detectability and sizing ability of RPC technique for axial or circumferential cracks at the tube expansion region. The simulated cracks with various dimensions were fabricated by electro-discharge machining (EDM) method. Experimental results are discussed with theoretical calculations.

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Estimates of Elastic Fracture Mechanics Parameters for Thick-Walled Pipes with Slanted Axial Through-Wall Cracks (두꺼운 배관에 존재하는 축방향 경사관통균열의 탄성파괴역학 매개변수 계산)

  • Han, Tae-Song;Huh, Nam-Su
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.12
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    • pp.1521-1528
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    • 2012
  • The present paper provides the elastic stress intensity factors (SIFs) and the crack opening displacements (CODs) of a thick-walled pipe with a slanted axial through-wall crack. For estimating these elastic fracture mechanics parameters, systematic three-dimensional elastic finite element (FE) analyses were performed by considering geometric variables, i.e., thickness of pipe, reference crack length, and crack length ratio, affecting the SIFs and CODs. As for loading condition, the internal pressure was considered. Based on the FE results, the SIFs and CODs of slanted axial through-wall cracks in a thickwalled pipe along the crack front and the wall thickness were calculated. In particular, to calculate the SIFs of a thick-walled pipe with a slanted axial through-wall crack from those of a thick-walled pipe with an idealized axial through-wall crack, a slant correction factor representing the effect of the slant crack on the SIFs was proposed.